The annex was built along the roundhouse to serve as a storage and service area. During its life portions of the building housed a morgue, the B&O’s Company library and a printing plant used to create many of the railroad’s publicity material, forms, timetables, and other publications. It has been modified and expanded several times to its current size and appearance. Today it serves as the Museum’s main entrance and includes the Alex Brown Exhibition Gallery, gift shop, and general offices.